Two Networks on one System

[n j]

I can't really say I understand the exact problem the OP has, but if
it's anything similar to asymmetrical/source-based routing problems I
was having some time ago, pf and reply-to is probably the best way to
do it. However, I'd also like to point out setfib(1), as it seems
no-one has brought it up yet, though there were statements like "there
can be only one default gw".

I was actually quite disappointed with lack of proper solution for
this problem on FreeBSD as it is so simple to set up on Linux.

Regards,
-- 
Nino